Method for performing measurement and device supporting the same

ABSTRACT

Provided are a method of performing measurement and a device supporting the method. According to one embodiment of the present invention, a method for performing measurement in a wireless communication system includes: receiving a first indication of the measurement from a serving cell; performing the measurement on neighbor cells; determining that the UE has a valid measurement result, based on a preconfigured threshold; and transmitting a second indication indicating that UE has the valid measurement result to the serving cell, based on the first indication.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119 (e), this application claims the benefit ofU.S. Provisional Application No. 62/529,477 filed on Jul. 7, 2017, thecontents of which are all hereby incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method performing measurement by a UE, and adevice supporting the same.

Related Art

Efforts have been made to develop an improved 5th-generation (5G)communication system or a pre-5G communication system in order tosatisfy a growing demand on radio data traffic after commercializationof a 4th-generation (4G) communication system. A standardization act fora 5G mobile communication standard work has been formally started in3GPP, and there is ongoing discussion in a standardization working groupunder a tentative name of a new radio access (NR).

Meanwhile, an upper layer protocol defines a protocol state toconsistently manage an operational state of a user equipment (UE), andindicates a function and procedure of the UE in detail. In thediscussion on the NR standardization, an RRC state is discussed suchthat an RRC_CONNECTED state and an RRC_IDLE state are basically defined,and an RRC_INACTIVE state is additionally introduced.

Meanwhile, in carrier aggregation (CA) or dual multiple connectivity(DC), a serving cell may need to add SCells which have good qualities.To find suitable SCells, the serving cell should indicate UE to measureneighbor cells. Then, the UE may measure qualities of neighbor cells,and report the result of the measurement.

SUMMARY OF THE INVENTION

According to a prior art, a UE is configured to transmit wholeinformation on measurement result to the network, so it requires much UEpower consumption.

According to one embodiment of the present invention, a method forperforming, by a user equipment (UE), measurement in a wirelesscommunication system is provided. The method comprises receiving a firstindication of the measurement from a serving cell; performing themeasurement for neighbor cells; determining that the UE has a validmeasurement result, based on a preconfigured threshold; and transmittinga second indication indicating that UE has the valid measurement resultto the serving cell, based on the first indication.

The valid measurement result may be better than the preconfiguredthreshold.

The measurement may be performed in RRC IDLE state or RRC INACTIVEstate.

The second indication may be transmitted during radio resource control(RRC) connection establishment procedure.

The method may further comprise transmitting the valid measurementresult to the network, upon receiving a request of the valid measurementresult from the network.

The valid measurement result may be transmitted via radio resourcecontrol (RRC) connection setup complete message or RRC connection resumecomplete message.

The valid measurement result may be used to add SCells for carrieraggregation (CA) or dual connectivity (DC) by the serving cell.

The first indication may be broadcasted via system information.

The first indication may be transmitted via a paging message includingidentity of the UE.

According to another embodiment of present invention, a user equipment(UE) in a wireless communication system is provided. The UE comprises atranceiver for transmitting or receiving a radio signal; and a processorcoupled to the transceiver, the processor configured to: receive a firstindication of the measurement from a serving cell; perform themeasurement for neighbor cells; determine that the UE has a validmeasurement result, based on a preconfigured threshold; and transmit asecond indication indicating that UE has the valid measurement result tothe serving cell, based on the first indication.

The valid measurement result may be better than the preconfiguredthreshold.

The measurement may be performed in RRC IDLE state or RRC INACTIVEstate.

The second indication may be transmitted during radio resource control(RRC) connection establishment procedure.

The processor may be further configured to transmit the validmeasurement result to the network, upon receiving a request of the validmeasurement result from the network.

The valid measurement result may be transmitted via radio resourcecontrol (RRC) connection setup complete message or RRC connection resumecomplete message.

The valid measurement result may be used to add SCells for carrieraggregation (CA) or dual connectivity (DC) by the serving cell.

The first indication may be broadcasted via system information.

The first indication may be transmitted via a paging message includingidentity of the UE.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of a control plane protocol stack of an LTEsystem.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem.

FIG. 4 shows a structure of a 5G system.

FIG. 5 shows an example of a method for performing measurement accordingto an embodiment of the present invention.

FIG. 6 shows an example of a method for performing measurement accordingto an embodiment of the present invention.

FIG. 7 shows another example of a method for performing measurementaccording to an embodiment of the present invention.

FIG. 8 shows an example of a method for performing measurement accordingto an embodiment of the present invention.

FIG. 9 shows an example of a method for performing measurement accordingto an embodiment of the present invention.

FIG. 10 shows a communication system to implement an embodiment of thepresent invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN may include at least one evolved node-B (eNB) 20, and aplurality of UEs may be present in one cell. An E-UTRAN system is asystem evolved from the existing UTRAN system, and may be, for example,a 3GPP LTE/LTE-A system. The E-UTRAN consists of base stations (BSs) (oreNBs) which provide the UE with control plane and user plane protocols,and the BSs are connected through an X2 interface. An X2 user plane(X2-U) interface is defined between the BSs. The X2-U interface providesnon-guaranteed delivery of a user plane packet data unit (PDU). An X2control plane (X2-CP) interface is defined between two neighboring BSs.The X2-CP performs a function of context delivery between BSs, userplane tunnel control between a source BS and a target BS,handover-related message delivery, uplink load management, or the like.The BS is connected to the UE through a radio interface, and isconnected to an evolved packet core (EPC) through an S1 interface. An S1user plane (S1-U) interface is defined between the BS and a servinggateway (S-GW). An S1 control plane (S1-MME) interface is definedbetween the BS and a mobility management entity (MME). The S1 interfaceperforms an evolved packet system (EPS) bearer service managementfunction, a non-access stratum (NAS) signaling transport function,network sharing, an MME load balancing function, or the like. The S1interface supports a many-to-many relation between the BS and theMME/S-GW.

The eNB 20 provides the UE with end points of the control plane and theuser plane. The eNB 20 is generally a fixed station that communicateswith the UE 10 and may be referred to as another terminology, such as abase station (BS), a base transceiver system (BTS), an access point, orthe like. One eNB 20 may be arranged in every cell. At least one cellmay be present in a coverage of the eNB 20. One cell is configured tohave one of bandwidths selected from 1.25, 2.5, 5, 10, and 20 MHz, etc.,and provides downlink (DL) or uplink (UL) transmission services toseveral UEs. In this case, different cells may be configured to providedifferent bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 areconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

The eNB 20 may perform functions of selection for gateway 30, routingtoward the gateway 30 during a radio resource control (RRC) activation,scheduling and transmitting of paging messages, scheduling andtransmitting of broadcast channel (BCH) information, dynamic allocationof resources to the UEs 10 in both UL and DL, configuration andprovisioning of eNB measurements, radio bearer control, radio admissioncontrol (RAC), and connection mobility control in LTE_ACTIVE state. Inthe EPC, and as noted above, gateway 30 may perform functions of pagingorigination, LTE_IDLE state management, ciphering of the user plane, SAEbearer control, and ciphering and integrity protection of NAS signaling.

FIG. 2 shows a block diagram of a control plane protocol stack of an LTEsystem, and FIG. 3 shows a block diagram of a user plane protocol stackof an LTE system.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data is transferred throughthe physical channel using radio resources. The physical channel ismodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARQ) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

A physical channel consists of a plurality of subframes in time domainand a plurality of subcarriers in frequency domain. One subframeconsists of a plurality of symbols in the time domain. One subframeconsists of a plurality of resource blocks (RBs). One RB consists of aplurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use specific subcarriers of specific symbols of acorresponding subframe for a PDCCH. For example, a first symbol of thesubframe may be used for the PDCCH. The PDCCH carries dynamic allocatedresources, such as a physical resource block (PRB) and modulation andcoding scheme (MCS). A transmission time interval (TTI) which is a unittime for data transmission may be equal to a length of one subframe. Thelength of one subframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel. A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom an upper layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

A non-access stratum (NAS) layer above the RRC layer performs functions,such as session management and mobility management.

Hereinafter, a 5G network structure is described.

FIG. 4 shows a structure of a 5G system.

In case of an evolved packet core (EPC) having a core network structureof the existing evolved packet system (EPS), a function, a referencepoint, a protocol, or the like is defined for each entity such as amobility management entity (MME), a serving gateway (S-GW), a packetdata network gateway (P-GW), or the like.

On the other hand, in case of a 5G core network (or a NextGen corenetwork), a function, a reference point, a protocol, or the like isdefined for each network function (NF). That is, in the 5G core network,the function, the reference point, the protocol, or the like is notdefined for each entity.

Referring to FIG. 4, the 5G system structure includes at least one UE10, a next generation-radio access network (NG-RAN), and a nextgeneration core (NGC).

The NG-RAN may include at least one gNB 40, and a plurality of UEs maybe present in one cell. The gNB 40 provides the UE with end points ofthe control plane and the user plane. The gNB 40 is generally a fixedstation that communicates with the UE 10 and may be referred to asanother terminology, such as a base station (BS), a base transceiversystem (BTS), an access point, or the like. One gNB 40 may be arrangedin every cell. At least one cell may be present in a coverage of the gNB40.

The NGC may include an access and mobility function (AMF) and a sessionmanagement function (SMF) which are responsible for a function of acontrol plane. The AMF may be responsible for a mobility managementfunction, and the SMF may be responsible for a session managementfunction. The NGC may include a user plane function (UPF) which isresponsible for a function of a user plane.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the gNB 40 may be connected by means of a Uu interface.The gNBs 40 may be interconnected by means of an X2 interface.Neighboring gNBs 40 may have a meshed network structure based on an Xninterface. The gNBs 40 may be connected to an NGC by means of an NGinterface. The gNBs 40 may be connected to an AMF by means of an NG-Cinterface, and may be connected to a UPF by means of an NG-U interface.The NG interface supports a many-to-many-relation between the gNB 40 andthe AMF/UPF 50.

A gNB host may perform functions such as functions for radio resourcemanagement, IP header compression and encryption of user data stream,selection of an AMF at UE attachment when no routing to an AMF can bedetermined from the information provided by the UE, routing of userplane data towards UPF(s), scheduling and transmission of pagingmessages (originated from the AMF), scheduling and transmission ofsystem broadcast information (originated from the AMF or O&M), ormeasurement and measurement reporting configuration for mobility andscheduling.

An access and mobility function (AMF) host may perform primary functionssuch as NAS signalling termination, NAS signalling security, AS securitycontrol, inter CN node signalling for mobility between 3GPP accessnetworks, idle mode UE reachability (including control and execution ofpaging retransmission), tracking area list management (for UE in idleand active mode), AMF selection for handovers with AMF change, accessauthentication, or access authorization including check of roamingrights.

A user plane function (UPF) host may perform primary functions such asanchor point for Intra-/inter-RAT mobility (when applicable), externalPDU session point of interconnect to data network, packet routing &forwarding, packet inspection and user plane part of policy ruleenforcement, traffic usage reporting, uplink classifier to supportrouting traffic flows to a data network, branching point to supportmulti-homed PDU session, QoS handling for user plane, e.g. packetfiltering, gating, UL/DL rate enforcement, uplink traffic verification(SDF to QoS flow mapping), transport level packet marking in the uplinkand downlink, or downlink packet buffering and downlink datanotification triggering.

A session management function (SMF) host may perform primary functionssuch as session management, UE IP address allocation and management,selection and control of UP function, configuring traffic steering atUPF to route traffic to proper destination, controlling part of policyenforcement and QoS, or downlink data notification.

Hereinafter, an RRC_INACTIVE State of a UE is Described.

In the discussion on the NR standardization, an RRC_INACTIVE state (RRCinactive state) has been newly introduced in addition to the existingRRC_CONNETED state and RRC_IDLE state. The RRC_INACTIVE state may be aconcept similar to a lightly connected mode which is under discussion inLTE. The RRC_INACTIVE state is a state introduced to efficiently managea specific UE (for example, mMTC UE). A UE in the RRC_INACTIVE stateperforms a radio control procedure similarly to a UE in the RRC_IDLEstate in order to reduce power consumption. However, the UE in theRRC_INACTIVE state maintains a connection state between the UE and anetwork similarly to the RRC_CONNECTED state in order to minimize acontrol procedure required when transitioning to the RRC_CONNECTEDstate. In the RRC_INACTIVE state, a radio access resource is released,but wired access may be maintained. For example, in the RRC_INACTIVEstate, the radio access resource is released, but an NG2 interfacebetween a gNB and am NGC or an S1 interface between an eNB and an EPCmay be maintained. In the RRC_INACTIVE state, a core network recognizesthat the UE is normally connected to a BS. On the other hand, the BS maynot perform connection management for the UE in RRC_INACTIVE state.

Hereinafter, IDLE measurement in LTE is described.

When evaluating Srxlev and Squal of non-serving cells for reselectionpurposes, the UE shall use parameters provided by the serving cell.Following rules are used by the UE to limit needed measurements:

If the serving cell fulfils Srxlev>SIntraSearchP andSqual>SIntraSearchQ, the UE may choose not to perform intra-frequencymeasurements.

Otherwise, the UE shall perform intra-frequency measurements.

The UE shall apply the following rules for E-UTRAN inter-frequencies andinter-RAT frequencies which are indicated in system information and forwhich the UE has priority:

For an E-UTRAN inter-frequency or inter-RAT frequency with a reselectionpriority higher than the reselection priority of the current E-UTRAfrequency the UE shall perform measurements of higher priority E-UTRANinter-frequency or inter-RAT frequencies.

For an E-UTRAN inter-frequency with an equal or lower reselectionpriority than the reselection priority of the current E-UTRA frequencyand for inter-RAT frequency with lower reselection priority than thereselection priority of the current E-UTRAN frequency:

If the serving cell fulfils Srxlev>SnonIntraSearchP andSqual>SnonIntraSearchQ, the UE may choose not to perform measurements ofE-UTRAN inter-frequencies or inter-RAT frequency cells of equal or lowerpriority unless the UE is triggered to measure an E-UTRANinter-frequency which is configured with redistributionInterFreqInfo.

Otherwise, the UE shall perform measurements of E-UTRANinter-frequencies or inter-RAT frequency cells of equal or lowerpriority.

The UE reports measurement information in accordance with themeasurement configuration as provided by E-UTRAN. E-UTRAN provides themeasurement configuration applicable for a UE in RRC_CONNECTED by meansof dedicated signalling, i.e. using the RRCConnectionReconfiguration orRRCConnectionResume message. The UE can be requested to perform thefollowing types of measurements:

Intra-frequency measurements: measurements at the downlink carrierfrequency(ies) of the serving cell(s).

Inter-frequency measurements: measurements at frequencies that differfrom any of the downlink carrier frequency(ies) of the serving cell(s).

Inter-RAT measurements of UTRA frequencies.

Inter-RAT measurements of GERAN frequencies.

Inter-RAT measurements of CDMA2000 HRPD or CDMA2000 1×RTT or WLANfrequencies.

CBR measurements.

Hereinafter, measurements in NR is described.

For the cell level mobility driven by RRC, the baseline of the RRMmeasurement framework for DL is the one specified for LTE (measurementobject, measurement ID, reporting configuration). The DL RRM measurementshould be performed based on a common framework regardless of networkand UE beam configurations (e.g. number of beams). As for the eventtriggered reporting, Event A1 to A6 like the ones specified for LTE areat least to be supported with potential modifications. Other events mayalso be studied for NR. Measurement report contains at least cell levelmeasurement results.

A UE in RRC_CONNECTED should be able to perform RRM measurements onalways on idle RS (e.g. NR-PSS/SSS) and/or CSI-RS. The gNB should beable to configure RRM measurements via dedicated signalling to beperformed on CSI-RS and/or idle RS. The event triggered reporting can beconfigured for NR-PSS/SSS and for CSI-RS for RRM measurements. At least,Even A1 to A6 can be configured for NR-PSS/SSS. It is FFS which eventscan be configured for CSI-RS.

In the multi-beam operation, the UE in RRC_CONNECTED measures at leastone or more individual DL beams. The gNB should have the mechanisms toconsider the measurement results of those DL beams for handover. Thismechanism is needed at least to trigger inter-gNB handover and tooptimise handover ping-pong and failure. The UE should be able todistinguish between the beams from its serving cell and the beams fromneighbour cells. The UE should be able to learn if a beam is coming fromits serving cell. Cell level signalling quality for the DL RRMmeasurement can be derived from N best beams, if detected, where thevalue of N can be configured to 1 or more than 1. This does not precludethe DL RRM measurement on a single beam. Measurement report may containthe measurement results of the N best beams if the UE is configured todo so by the gNB.

Meanwhile, in carrier aggregation (CA) or dual multiple connectivity(DC), a serving cell may need to add SCells which have good qualities.To find suitable SCells, the serving cell should indicate UE to measureneighbor cells. Then, the UE may measure qualities of neighbor cells,and report the result of the measurement. In this case, it takes time toreport measurement result upon RRC connection procedure is completed. IfUE reports measurement results of neighbor cells to the serving cellupon RRC connection setup, the serving cell is able to start carrieraggregation or dual multiple connectivity by adding SCells immediatelyto the UE based on the reported measurement results. However, UE in IDLEstate or INACTIVE state doesn't know when to establish RRC connection.So it is undesirable that the UE always performs neighbor cellmeasurement during IDLE state or INACTIVE state, because it is enoughthat if the measurement for carrier aggregation (CA) or dualconnectivity (DC) is performed shortly before RRC connection setup.

Hereinafter, a method for performing measurement for a neighbor cell bya UE in IDLE state or INACTIVE state according to an embodiment ofpresent invention is provided. In this description, the measurementaccording to an embodiment of present invention may be referred as anadditional measurement. The additional measurement may be performed foradding SCells in CA or DC, in addition to conventional measurements. Theadditional measurement may be performed in case that RRC connectionprocedure begins, so that the UE may report the measurement result assoon as the RRC connection procedure is completed. At the same time, theadditional measurement may be performed in restricted condition, so thatthe UE may avoid the case that the UE always performs neighbor cellmeasurement during IDLE state or INACTIVE state. Further, when the UEhas valid measurement results upon performing the additionalmeasurement, then the UE may notify it to the network. According to anembodiment of present invention, the UE may initiate the additionalmeasurement if upper layers, such as NAS layer, request establishment orresume of an RRC connection while the UE is in RRC_IDLE or RRC_INACTIVE,or if it receives paging message including its identity and/or if itreceives the additional measurement indication. Then the UE may reportthe results of the additional measurement to serving cell during orshortly after RRC connection establishment procedure. Thus, whenentering RRC_CONNECTED state, the UE is able to report the measurementresults to network immediately with the minimum of UE power consumptionfor neighbor cell measurement.

According to an embodiment of present invention, when the UE in IDLEstate or INACTIVE state receives paging message related to mt-call, theNAS layer of the UE may request establishment or resume of an RRCconnection. In this case, the UE may initiate performing measurement forneighbor cells, when the NAS layer requests establishment or resume ofan RRC connection or when the UE receives paging message which causedinitiating RRC connection procedure.

The UE in IDLE state or INACTIVE state may initiate the additionalmeasurement upon receiving the additional measurement indication from anetwork. The additional measurement indication can be provided viapaging message. Further, the paging message may include the additionalmeasurement indication and identity of the UE. The additionalmeasurement indication may be signaled per UE or per a group of UEs.Alternatively, the additional measurement indication may be broadcasted,e.g. via system information. The UE may initiate the additionalmeasurement if upper layers request establishment or resume of anRRC_connection and the additional measurement indication is broadcastfrom serving cell.

Further, the UE may receive an additional measurement configuration. TheUE may perform the additional measurement in accordance with theadditional measurement configuration. The UE may receive the additionalmeasurement configuration when leaving RRC_CONNECTED state, e.g. via RRCConnection Release message or RRC Connection Resume message.Alternatively, the UE may receive the additional measurementconfiguration in broadcast manner, e.g. via system information.Alternatively, there may be no separate additional measurementconfiguration. In this case, the UE may perform the additionalmeasurement in accordance with normal measurement configuration in IDLEstate or INACTIVE state which is broadcasted via system information.

If available RRC connection establishment or resume cause is included inthe additional measurement configuration, the UE may initiate theadditional measurement only when it is going to establish RRC connectiondue to an establishment or resume cause which is indicated in theadditional measurement configuration. Desirably, UE may initiate theadditional measurement when MAC layer starts random access channel(RACH) procedure, e.g. upon sending MSG1. Or, UE may initiate theadditional measurement when RRC layer starts RRC connectionestablishment procedure, e.g. upon sending RRC connection setup request.According to an embodiment of present invention, if the additionalmeasurement configuration indicates only ‘mo-Data’ andestablishmentCause received from higher layers is set to ‘mo-Signaling’then the UE may not initiate the additional measurement. According toanother embodiment of present invention, if the additional measurementconfiguration indicates only ‘mt-Data’ and establishmentCause receivedfrom higher layers is set to ‘mt-Data’, then the UE may initiate theadditional measurement.

Though some threshold has been configured for the UE to restrict theneighbor cell measurement when serving cell quality is good, the UE mayperform the additional measurement regardless of the serving cellquality. In prior art, measurement for neighbor cell is performed when aspecific condition, such as the condition that a serving cell quality isworse than the threshold, is met. However, according to an embodiment ofpresent invention, the UE may perform the measurement for neighbor cellwhen the UE receives the request of establishment or resume of the RRCconnection, or when the UE receives additional measurement indication,regardless of the serving cell quality. If measurement object isincluded in the additional measurement configuration, the UE may performthe additional measurement only for the frequency of cell indicated bythe measurement object.

If report event is included in the additional measurement configuration,the UE may report the additional measurement results only when thereport event is satisfied for some measured cell. If report event isincluded in the additional measurement configuration, the UE may reportthe additional measurement results only for cell for which the reportevent is satisfied. For example, the UE may report the result ofmeasurement, when the serving cell quality is worse than threshold 1 andneighbor cell is better than threshold 2.

UE may stop the additional measurement if it acquire availablemeasurement results to report, or after reporting the measurementresults to serving cell.

FIG. 5 shows an example of a method for performing measurement accordingto an embodiment of the present invention. In this embodiment of presentinvention, the UE is in RRC_IDLE state as an initial state.

In step S502, the UE in RRC_IDLE state changes serving cell byperforming cell reselection procedure.

In step S504, the UE may send the system information requests to acquireadditional measurement configuration.

In step S506, the UE may receive the additional measurementconfiguration. The additional measurement configuration may include atleast one of measurement object, report event and establishment orresume cause. For example, the measurement object may be carrierfrequency #1, #2 and #4. The report event may indicate that neighbor isbetter than threshold. The establishment or resume cause may be mo-Dataand mt-Access.

In step S508, upon receiving the paging message including UE identity(ID) and additional measurement indication, UE may initiate theadditional measurement. According to the example, the UE may measurefrequency #1, #2 and #4 regardless of serving cell quality. Then, the UEmay find two cells, cell S and cell W, for which the report event issatisfied. On the other hands, the UE may initiate the additionalmeasurement, when the upper layers request establishment or resume ofRRC connection according to the paging message.

In step S510, the UE may initiate RRC connection establishment procedurewith establishmentCause ‘mt-Access’.

In step S512, the UE may receive RRC connection setup message from theserving cell.

In step S514, the UE may include the additional measurement results ofcell S and cell W to the RRC connection message and send it to theserving cell.

FIG. 6 shows an example of a method for performing measurement accordingto an embodiment of the present invention.

In step S602, the UE may receive a request of establishment or resume ofa radio resource control (RRC) connection from an upper layer. The upperlayer may be non-access stratum (NAS) layer of the UE. The UE may be inRRC IDLE state or RRC INACTIVE state. In step S604, the UE may performthe measurement for neighbor cell according to the request.

Further, the UE may report a result of the measurement to a servingcell, via a RRC connection complete message from a serving cell. Theresult of the measurement may be used to add SCells for carrieraggregation (CA) or dual connectivity (DC) by the serving cell. The UEmay further receive a measurement configuration via system information.The measurement configuration may include at least one of a measurementobject, reporting events and establishment or resume of RRC connectioncause.

FIG. 7 shows another example of a method for performing measurementaccording to an embodiment of the present invention.

In step S702, the UE may receive a paging message including identity ofthe UE from a network. The UE may be in RRC IDLE state or RRC INACTIVEstate. The paging message may be related to a mobile terminated (MO)call. The UE may report a result of the measurement to a serving cell,via a RRC connection complete message. The result of the measurement maybe used to add SCells for carrier aggregation (CA) or dual connectivity(DC) by the serving cell. In step S704, the UE may perform themeasurement for neighbor cell, upon receiving the paging message.

Further, the UE may receive an indication of measurement from thenetwork. The UE may further receive a measurement configuration viasystem information. The measurement configuration may include at leastone of a measurement object, reporting events and establishment orresume of RRC connection cause.

According to another aspect of present invention, if the UE has validmeasurement results after performing the additional measurement, thenthe UE may notify it to the network (for example, eNB or gNB). Inspecific, during RRC connection establishment procedure, UE may indicatewhether it has valid measurement results of the additional measurementto network, e.g. via MSG3 (=RRC Connection setup request or resumerequest message). In this embodiment of present invention, validmeasurement results may indicate measurement results which are betterthan a preconfigured threshold value among measurement results of theadditional measurement. During RRC connection establishment procedure,if UE receives the additional reporting indication from network and ithas valid measurement results of the additional measurement, the UE mayreport the additional measurement results to the network. The additionalreporting indication may be included in the MSG4 (=RRC connectionsetup/resume message). The additional measurement results may beincluded in the MSG5 (=RRC connection setup/resume complete message).Desirably, the additional reporting indication may be included in MAC CEin MSG2. In this case, the additional measurement results may bereported to network via MSG 3. Each of the above-described messages isfor understanding purposes, and is not limited to a specific message.However, according to embodiments of present invention, the messages maybe one of messages used in RRC connection procedure.

FIG. 8 shows an example of a method for performing measurement,according to an embodiment of the present invention.

In step S802, the UE may transmit MSG1. Upon transmitting the MSG1, UEmay initiate the additional measurement.

In step S804, the UE may receive MSG2.

In step S806, the UE may transmit the valid measurement indication tothe network. The valid measurement indication may indicate whether theUE has valid measurement results or not. In other words, the validmeasurement indication may indicate whether the UE has measurementresults to report or not. That is, in this description, whether the UEhas measurement results to report or not may be one of measurementreporting conditions. Thus, the valid measurement indication may be usedfor notifying the network of that the report of measurement result isavailable. If the UE has valid measurement results of the additionalmeasurement, UE may set the valid measurement indication to TRUE. Ifnot, the UE may set it to FALSE. The UE may transmit the validmeasurement indication to the network during RRC establishmentprocedure. For example, the UE may transmit the valid measurementindication via RRC connection request message, RRC connection setupcomplete message or RRC connection resume complete message. Morespecifically, if the UE receives the additional measurement indicationand the UE has valid measurement results of the additional measurement,the UE may transmit the valid measurement indication to the network.

In step S808, the UE may receive additional reporting indication fromthe network. The additional reporting indication may indicate that thenetwork inquires the UE to transmit the results of additionalmeasurement. The additional reporting indication may be included in RRCconnection setup message.

In step S810, if the UE receives the additional reporting indication,the UE may report the additional measurement results via MSG5. MSG5 maybe one of RRC connection setup complete message or RRC connection resumecomplete message. If not, the UE doesn't report the additionalmeasurement results.

FIG. 9 shows an example of a method for performing measurement,according to an embodiment of the present invention.

In step S902, the UE may receive a first indication of the measurementfrom a serving cell. The first indication may be broadcasted via systeminformation. The first indication may be transmitted via a pagingmessage including identity of the UE.

In step S904, the UE may perform the measurement for neighbor cells. Themeasurement is performed in RRC IDLE state or RRC INACTIVE state. Instep S906, the UE may determine that the UE has a valid measurementresult, based on a preconfigured threshold. The valid measurement resultmay be better than the preconfigured threshold.

In step S908, the UE may transmit a second indication indicating that UEhas the valid measurement result to the serving cell, based on the firstindication. The second indication is transmitted during radio resourcecontrol (RRC) connection establishment procedure.

Further, the UE may transmit the valid measurement result to thenetwork, upon receiving a request of the valid measurement result fromthe network. The valid measurement result is transmitted via radioresource control (RRC) connection setup complete message or RRCconnection resume complete message. The valid measurement result is usedto add SCells for carrier aggregation (CA) or dual connectivity (DC) bythe serving cell.

FIG. 10 shows a communication system to implement an embodiment of thepresent invention.

A UE 1000 includes a processor 1001, a memory 1002, and a transceiver1003. The memory 1002 is coupled to the processor 1001, and stores avariety of information for driving the processor 1001. The transceiver1003 is coupled to the processor 1001, and transmits and/or receives aradio signal. The processor 1001 implements the proposed functions,procedures, and/or methods. In the aforementioned embodiments, anoperation of the first network node may be implemented by the processor1001.

A network node 1010 includes a processor 1011, a memory 1012, and atransceiver 1013. The memory 1012 is coupled to the processor 1011, andstores a variety of information for driving the processor 1011. Thetransceiver 1013 is coupled to the processor 1011, and transmits and/orreceives a radio signal. The processor 1011 implements the proposedfunctions, procedures, and/or methods. In the aforementionedembodiments, an operation of the second network node 1010 may beimplemented by the processor 1011.

The processors 1011 may include application-specific integrated circuit(ASIC), other chipset, logic circuit and/or data processing device. Thememories may include read-only memory (ROM), random access memory (RAM),flash memory, memory card, storage medium and/or other storage device.The transceivers may include baseband circuitry to process radiofrequency signals. When the embodiments are implemented in software, thetechniques described herein can be implemented with modules (e.g.,procedures, functions, and so on) that perform the functions describedherein. The modules can be stored in memories and executed byprocessors. The memories can be implemented within the processors orexternal to the processors in which case those can be communicativelycoupled to the processors via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for performing, by a user equipment(UE), measurement in a wireless communication system, the methodcomprising: receiving a first indication of the measurement from aserving cell; performing the measurement on neighbor cells; determiningthat the UE has a valid measurement result, based on a preconfiguredthreshold; and transmitting a second indication indicating that UE hasthe valid measurement result to the serving cell, based on the firstindication.
 2. The method of claim 1, wherein the valid measurementresult is better than the preconfigured threshold.
 3. The method ofclaim 1, wherein the measurement is performed in RRC_IDLE state orRRC_INACTIVE state.
 4. The method of claim 1, wherein the secondindication is transmitted during radio resource control (RRC) connectionestablishment procedure.
 5. The method of claim 1, further comprising:transmitting the valid measurement result to the network, upon receivinga request of the valid measurement result from the network.
 6. Themethod of claim 5, wherein the valid measurement result is transmittedvia radio resource control (RRC) connection setup complete message orRRC connection resume complete message.
 7. The method of claim 1,wherein the valid measurement result is used to add SCells for carrieraggregation (CA) or dual connectivity (DC) by the serving cell.
 8. Themethod of claim 1, wherein the first indication is broadcasted viasystem information.
 9. The method of claim 1, wherein the firstindication is transmitted via a paging message including identity of theUE.
 10. A user equipment (UE) in a wireless communication system, the UEcomprising: a tranceiver for transmitting or receiving a radio signal;and a processor coupled to the transceiver, the processor configured to:receive a first indication of the measurement from a serving cell;perform the measurement on neighbor cells; determine that the UE has avalid measurement result, based on a preconfigured threshold; andtransmit a second indication indicating that UE has the validmeasurement result to the serving cell, based on the first indication.11. The UE of claim 10, wherein the valid measurement result is betterthan the preconfigured threshold.
 12. The UE of claim 10, wherein themeasurement is performed in RRC_IDLE state or RRC_INACTIVE state. 13.The UE of claim 10, wherein the second indication is transmitted duringradio resource control (RRC) connection establishment procedure.
 14. TheUE of claim 10, wherein the processor is further configured to: transmitthe valid measurement result to the network, upon receiving a request ofthe valid measurement result from the network.
 15. The UE of claim 14,wherein the valid measurement result is transmitted via radio resourcecontrol (RRC) connection setup complete message or RRC connection resumecomplete message.
 16. The UE of claim 10, wherein the valid measurementresult is used to add SCells for carrier aggregation (CA) or dualconnectivity (DC) by the serving cell.
 17. The method of claim 10,wherein the first indication is broadcasted via system information. 18.The UE of claim 10, wherein the first indication is transmitted via apaging message including identity of the UE.